Climate Change Poised to Cause ‘Monster-Sized’ Algae Blooms in the St. Croix

The St. Croix River will get warmer and greener in the next few decades as climate change causes hotter, wetter springs and drier summers – ideal conditions for algae. The assessment is based on new data from the U.S. Geological Survey (USGS).

The USGS’s National Climate Change Viewer recently added the ability to analyze climate forecasts specifically for the area defined by the St. Croix and its tributaries. When Sue Magdalene of the Science Museum of Minnesota’s St. Croix Watershed Research Station looks at what is expected to change by the year 2050, she sees water quality problems already facing the river getting worse due to a combination of climate circumstances.

“We have all the conditions set up for slow flows during hot weather creating stagnant monster-sized algal blooms,” Magdalene says.

The primary concern is that, even though annual rainfall will increase, the region’s wet season will shift earlier in the year. This will mean more frequent floods, and the dry days of August and September will get even less rain. Slower current and lower water levels in late summer would set back efforts to reduce runoff and improve water quality.

“Even though we are making progress, and trends look good on phosphorus, it does not look good for algae,” Magdalene said. “The low flows we normally see in August are expected to get worse.”

And, while late summer will be drier, the early season could see increased precipitation, meaning more frequent floods. Precipitation is more difficult to predict than temperature, due to more variables affecting rainfall. But there is no disagreement in the science that the area will get hotter – at faster and faster rates. Magdalene points out that from 1950 to 2000, the region’s temperature increased by one degree. From 2000 to 2050, it will get five to six degrees warmer.

The USGS tool provides 30 different climate models, optimized for different regions or variables. All 30 predict warmer temperatures and 25 of the models predict slightly higher annual precipitation by 2050.